The present invention relates to the field of torque converters, and more particularly relates to the field of torque converters equipped with lock up clutches which incorporate rotary dampers.
It is well known for a fluid torque converter, which comprises a pump impeller coupled to a power input shaft, a turbine connected to a power output shaft, and a stator, and in which by fluid circulation through the pump impeller, the turbine, and the stator rotary power is transmitted between said pump impeller and said turbine, so that this rotary power is transmitted from said power input shaft to said power output shaft, to be provided with a lock up clutch. Such a lock up clutch is arranged so as directly mechanically to connect the power input shaft to the power output shaft, selectively, and the selective engagement of this direct engagement clutch is performed according to the operational conditions of the vehicle to which this torque converter is fitted. In general, such a lock up clutch is engaged when the torque converter is required to transmit rotary power at high rotational speed, at which time the torque conversion function of the torque converter is not substantially required. In such a case, if the lock up clutch is not engaged, then, although the torque converter provides a substantially direct power transmission function between its pump impeller and its turbine, a small amount, such as a few percent, of slippage between the pump impeller and the turbine will inevitably occur, and this wastes a substantial amount of energy through the useless circulation of hydraulic fluid, and also causes undesirable heating up of the hydraulic fluid within the torque converter.
When such a lock up clutch is provided for a fluid torque converter, the problem arises that, when the lock up clutch is engaged from the disengaged condition, a substantial torque shock inevitably occurs, because before the lock up clutch is engaged, as explained above, there is inevitably a certain amount of slippage between the power input shaft and the power output shaft, and they are thus not rotating at exactly the same rotational speed at this time, due to the action of the torque converter. Further, during operation of the vehicle incorporating the torque converter while the lock up clutch is engaged, it often occurs that torque shock is transmitted along the power train. Therefore, it is usual to provide a rotary damper within the power train as part of the lock up clutch, so that such a torque shock can be effectively absorbed.
Such a rotary damper in general conventionally comprises two outer disk elements which are sandwiched on opposite sides of an inner disk element, the two outer disk elements being coupled together with respect to their rotation; and one of the power input shaft and the power output shaft is arranged to be rotationally coupled to said outer disk elements, while the other of them is arranged to be coupled to said inner disk element. The inner disk element is conventionally rotationally coupled to the outer disk elements with a certain amount of damped rotational free play, or cushioning, therebetween, in a way which will now be described.
In the inner disk element there are formed slot shaped apertures extending generally in the circumferential direction of said inner disk element, and within these slot apertures there are disposed compression coil springs whose axes lie generally in the plane of the inner disk element and in its circumferential direction. Corresponding to each of these springs, in the outer disk elements in positions opposing the springs, there are formed circumferentially extending slot shaped apertures, which typically are formed by making incisions shaped in the form of a capital letter "I" with serifs, the long portion of the "I" lying generally in the circumferential direction of the outer disk element. That is to say, each of these incisions is formed as one longer circumferentially extending incision, and two shorter radially extending end bar incisions, one at each of the ends of said longer incision. The thus formed flap portions are then bent outwards, in the direction of the side of the outer disk element of which they formed part which faces away from the inner disk element, at angles of approximately 45.degree., so that they may receive the sides of the aforesaid compression coil springs which rest within the slot shaped apertures formed in the inner disk element. Thus, the sides of these compression coil springs are received in so called troughs formed in the outer disk elements.
Thus, when the inner disk element is rotated relative to the combination of the outer disk elements, the one ends of these compression coil springs in the one direction of rotation abut against the ends of the circumferentially extending slot shaped apertures in the inner damper plate element, and the other ends of these compression coil springs abut against the other ends in the other circumferential direction of the slot shaped apertures thus formed in the outer damper plate elements, and accordingly by the compression of the compression coil springs torque shock is absorbed.
This construction minimizes the transmission of rotational torque shock between the power input shaft and the power output shaft; that is to say, in a vehicle incorporating the aforesaid torque converter, between the engine and the driven wheels thereof, when the lock up clutch is engaged from the disengaged condition. Such a conventional construction for a rotary damper for a lock up clutch for torque converter is satisfactory; but the cutting of these "I" shaped cutouts in the outer disk elements significantly weakens these outer disk elements. This is not very important when the radius of the rotary damper is small, because in this case the centrifugal force acting upon the portions thereof such as the compression coil springs is relatively small, even when the torque converter and the lock up clutch thereof are rotating at high rotational speed. However, when it is attempted to increase the radius of the rotary damper, problems are found with regard to the durability thereof, and with regard to centrifugal forces.